docs: def twovec(axdef, indexa, plndef, indexp):
      """
      Find the transformation to the right-handed frame having a
      given vector as a specified axis and having a second given
      vector lying in a specified coordinate plane.
  
      http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/twovec_c.html
  
      :param axdef: Vector defining a principal axis.
      :type axdef: 3-Element Array of floats
      :param indexa: Principal axis number of axdef (X=1, Y=2, Z=3).
      :type indexa: int
      :param plndef: Vector defining (with axdef) a principal plane.
      :type plndef: 3-Element Array of floats
      :param indexp: Second axis number (with indexa) of principal plane.
      :type indexp: int
      :return: Output rotation matrix.
      :rtype: 3x3-Element Array of floats
      """
      axdef = stypes.toDoubleVector(axdef)
      indexa = ctypes.c_int(indexa)
      plndef = stypes.toDoubleVector(plndef)
      indexp = ctypes.c_int(indexp)
      mout = stypes.emptyDoubleMatrix()
      libspice.twovec_c(axdef, indexa, plndef, indexp, mout)
      return stypes.cMatrixToNumpy(mout)